Method and device for measuring the power dissipated by a hydridation reaction in tubes and tubular claddings and the corresponding variation in electric resistance

ABSTRACT

The invention relates to a method and device for measuring hydridation kinetics at different temperatures in tubular industrial components. The invention consists in measuring the power dissipated by a hydridation reaction over time as well as the variation in the electric resistance during said reaction. The inventive method and device can be used to optimise industrial components, such as tubes and fuel claddings for nuclear reactor cores. In this way, safety is increased, with the prevention of unplanned shutdowns of commercial reactors and a decrease in high-activity nuclear waste.

RELATED APPLICATIONS

The present application is a Continuation of co-pending PCT ApplicationNo. PCT/ES2005/070011, filed Feb. 1, 2005 which in turn, claims priorityfrom Spanish Application Serial No. P200400294, filed on Feb. 9, 2004.Applicants claim the benefits of 35 U.S.C. §120 as to the PCTapplication and priority under 35 U.S.C. §119 as to said Spanishapplication, and the entire disclosures of both applications areincorporated herein by reference in their entireties.

SECTOR OF THE ART

Measurement of hydridation reactions and kinetics of tubes and tubularcladdings of metallic elements, metal alloys and any other material withand without protective coverings.

STATE OF THE ART

The massive hydridation of metallic industrial components is one of thecauses of their becoming brittle and can lead to catastrophic fracturedue to the formation of cracks. This process takes place in componentsin contact with water under pressure and/or boiling and at hightemperature, and can become acute when the component is exposed to highconcentrations of hydrogen as a consequence of other processes. A casethat has been known for some years is the hydridation of tubular fuelcladdings in the cores of nuclear reactors, which can take placemassively from inside the cladding in the event of loss of airtightnessas a result of a primary failure. Patent WO0223162 describes a methodand device for measuring the resistance to hydridation in these tubularcomponents in order to help in the selection of materials and designaimed at reducing these problems. Nevertheless, other measurements needto be determined in order to compare the hydridation kinetics, whichpermits the response to hydridation of the different elements and alloysof the tubular components to be compared and a choice to be made ofthose designs and compositions that will prevent or delay the appearanceof these fractures in metallic industrial components.

So far, the determination of the hydridation kinetics of metals andalloys has been carried out by thermogravimetry and morphologicalstudies of hydridation processes of pieces of material in an autoclave,which in some cases, as in the hydridation of fuel claddings, representsworking conditions that are very different from those in which thehydridation of the component is produced.

DESCRIPTION OF THE INVENTION BRIEF DESCRIPTION OF THE INVENTION

The present invention tackles the problem of providing new methods andtools for measuring the hydridation kinetics taking place in tubularcomponents for industrial use.

The solution provided by this invention permits measurement of thehydridation kinetics in the actual tubular components, generallymulti-layer, and under the same conditions of working temperature inwhich the hydridation of the component takes place, which is ofparticular economic relevance since it permits the design and choice ofthe appropriate composition of the different alloys used. Anoptimisation of these components will be able to help prevent unplannedshutdowns of commercial reactors. This possible improvement will alsoallow greater exploitation of the fuel by making it more robust, and adecrease in the mass of high-activity nuclear waste for the same amountof energy generated. By eliminating a possible source of leakage ofcomponents in the reactor water, the dosage of radiation received bymaintenance personnel and personnel having to perform operations in theexchange zone will be reduced.

So, the first object of this invention consists of a new method formeasuring hydridation kinetics at different temperatures, in industrialcomponents, wherein it consists of measuring: a) the power dissipated bythe hydridation reaction, hereinafter referred to as the dissipatedhydridation power (DHP), as a function of time, along with its integralas a function of time hereinafter referred to as the dissipatedhydridation energy (DHE), and b) the variation in electric resistanceduring that reaction, and in particular during the stage of dissolutionof hydrogen in the component preceding the precipitation of hydrides inthe material;

The second object of this invention consists of a device (FIG. 4) forcarrying out the aforementioned measurement method consisting of:

-   -   a) a high or ultra-high vacuum chamber in which the component to        be analysed is inserted,    -   b) a gas line for causing hydrogen or a mixture of hydrogen with        other gas(es) to pass through the interior of the component,    -   c) heating systems by the Joule effect, thermocouples and        systems for temperature control in the component, and    -   d) two electrodes in the form of a ring or other well-defined        geometry, arranged on the component symmetrically and        equidistant from the central thermocouple connected with the        outside of the device where the measurements are going to be        made.

Finally, the third object of this invention consists of the use of thesaid method and device for making measurements of hydridation kineticsin industrial components of metallic elements, metal alloys and anyother material with and without protective coverings, preferably tubularcomponents such as tubes and tubular claddings for fuel in the cores ofnuclear reactors.

DETAILED DESCRIPTION OF THE INVENTION

The first object of this invention consists of a new method formeasuring hydridation kinetics, herein after the inventive method, atdifferent temperatures, in industrial components of metallic elements,metal alloys and any other material with and without protectivecoverings, wherein it consists of measuring:

-   -   a) the power dissipated by the hydridation reaction, hereinafter        the dissipated hydridation power (DHP), as a function of time,        along with its integral as a function of time hereinafter        referred to as the dissipated hydridation energy (DHE),    -   b) the variation in electric resistance during that reaction,        and in particular during the stage of dissolution of hydrogen in        the component preceding the precipitation of hydrides in the        material; and because the stages making up this method are:    -   i) insertion of the tubular component in a high or ultra-high        vacuum chamber,    -   ii) circulation of hydrogen or a mixture of hydrogen with other        gas(es) through the interior of the component, it being the        permeation of the hydrogen via the wall of the component that        causes the hydridation of the material,    -   iii) heating of the component by the Joule effect,    -   iv) determination of the dissipated hydridation power as a        function of time, of the dissipated hydridation energy measured        during the process, and of the electric resistance in the        component by means of:        -   iv.1) the voltage drop along the component, and        -   iv.2) the variation in electric current applied for            maintaining its temperature at the predetermined value for            the hydridation reaction.

As used in the present invention, the term “industrial components”refers to tubular components, with a wall consisting of a single elementor with multi-layer wall, as are tubes and tubular claddings for fuel inthe cores of nuclear reactors.

The control of these industrial components by means of the inventivemethod will permit the design and choice of the suitable composition ofthe different alloys used for the manufacture of those components,thereby avoiding their fracture.

During the precipitation reaction and formation of hydrides, the heat ofreaction causes a drop in the electric current being applied in order tokeep the temperature constant, which leads to a decrease in the powernecessary for maintaining that temperature. The variation or differencein the necessary power corresponds to the dissipated hydridation power(DHP) and is roughly proportional to the hydride precipitated per unittime. This variation or decrease is measured as a function of time andpermits a comparison to be made of the hydridation kinetics incomponents of different structure and composition, which permits acriterion to be had for the choice of materials and design. During theprocess and by means of integration with respect to time, one obtainsthe energy dissipated in the hydridation reaction which is roughlyproportional to the quantity of hydride precipitated.

The second object of this invention consists of a device (FIG. 4),hereinafter the inventive device, for carrying out the inventivemeasurement method and which consists of:

-   -   a) a high or ultra-high vacuum chamber in which the component to        be analysed is inserted,    -   b) a gas line for causing hydrogen or a mixture of hydrogen with        other gas(es) to pass through the interior of the component,    -   c) heating systems by the Joule effect, thermocouples and        systems for temperature control in the component, and    -   d) two electrodes in the form of a ring or other well-defined        geometry, arranged on the component symmetrically and        equidistant from the central thermocouple connected with the        outside of the device where the measurements are going to be        made.

During the hydridation reaction, the temperature in the interior of thecomponent has to remain constant, for which a thermocouple and atemperature control system is used which acts on the current applied forheating the component (c). Moreover, in order to measure the voltagedrop, and consequently the variation in electric resistance and thepower dissipated during the hydridation reaction along the componentduring said reaction, the two electrodes are used arranged on thecomponent (d)

Finally, the third object of this invention consists of the use of theinventive method and device for making measurements of hydridationkinetics in industrial components of metallic elements, metal alloys andany other material with and without protective coverings, preferablytubular components such as tubes and tubular claddings for fuel in thecores of nuclear reactors.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1. Variation in electric resistance during the hydridation process.Following the variation in electric resistance owing to the increase intemperature, the first stage of growth, and once the temperature of theexperiment has been reached, a sharp growth takes place, marked betweenthe arrows, due to the dissolution of H in the metal, and the finalmaximum of this stage roughly coincides with the start of theprecipitation of H in the form of hydrides.

FIG. 2. Variation in dissipated hydridation power. Once the temperatureof the experiment has been reached, the DHP remains constant for a shortinterval, the incubation time, during which the H is dissolved withoutprecipitating. Once that period has passed coinciding with the growth ofelectric resistance, the DHP grows rapidly, corresponding to the startof precipitation of H in the form of hydrides in the material.

FIG. 3. Variation in dissipated hydridation energy. This corresponds tothe integral of FIG. 2.

FIG. 4. Diagram of the hydridation kinetics measurement device. Thisshows the position of the electrodes used for measuring the voltage dropin the tube.

EXAMPLES OF EMBODIMENT OF THE INVENTION Example 1 Measurement of theHydridation Kinetics in Tubes or Tubular Claddings

A method for measuring the dissipated power and the electric resistanceand thereby obtain the hydridation kinetics in tubes or tubularcladdings is embodied as stated below.

A nuclear fuel cladding of Zircaloy 2 is inserted in a high orultra-high vacuum chamber; hydrogen or mixtures of hydrogen with othergas(es) is made to circulate via the interior of the tube at a pressureof 1 atmosphere and a renewal stream of 200 cm³ per minute. The partialpressure in the vacuum zone is 10⁻⁹ Torr owing to the permeation ofhydrogen through the walls of the cladding. The cladding is heated bythe Joule effect and the temperature in the centre of the cladding ismonitored and kept constant at 360° C. (or other pre-established value)with a thermocouple and a temperature control system which acts on thecurrent being applied in order to heat the cladding, the amount ofcurrent needed in order to maintain a constant temperature of 360° C. inthe absence of reaction being 30 A. The electrodes, located on bothsides of the thermocouple, provide a measurement of the voltage drop inthe cladding during the hydridation reaction. Together with themeasurement of the current applied, this permits us to obtain the valueof the power necessary for keeping the temperature constant, and tomeasure the electric resistance of the cladding. When the dilution ofthe hydrogen in the cladding starts, the electric resistance can grow upto 3% (FIG. 1), though this variation can be less if the claddingpreviously contains a quantity of hydrogen, and no major changes areobserved in the power necessary for keeping the temperature constant.When the precipitation and the formation of hydride starts, the heat ofreaction means that the power necessary for keeping the temperatureconstant decreases, the difference in which gives us the value of DHPand, by integration, the dissipated hydridation energy or DHE. The DHPis roughly proportional to the hydride precipitated per unit time andthe DHE to the total quantity of precipitated hydride. By stopping theprocess at different value of DHE, samples can be obtained withdifferent thicknesses of the hydrides ring. These samples are veryuseful for mechanical studies and studies of the geometry of theprecipitated hydrides. The comparison of the DHP curves permits acriterion to be had for selection of materials and design. FIG. 1 showsthe variation curve of electric resistance, in which the first maximumcorresponds to the end of the dissolution process of hydrogen and thefinal maximum corresponds to the end of the hydridation process. FIG. 2shows the DHP curve, in which the maximum indicates that theprecipitation reaction is very rapid at the start of the process. FIG. 3corresponds to the DHE curve.

1. Method for measuring hydridation kinetics, at different temperatures,in industrial components such as tubes and tubular claddings of metallicelements, metal alloys and any other material with and withoutprotective coverings, wherein it consists of the measurement of: a) thepower dissipated by the hydridation reaction, hereinafter dissipatedhydridation power, as a function of time, and of the dissipatedhydridation energy, measured during the process, and b) the variation inelectric resistance during that reaction, and in particular during thestage of dissolution of hydrogen in the component preceding theprecipitation of hydrides in the material. the stages making up thismethod being: i) insertion of the tubular component in a high orultra-high vacuum chamber, ii) circulation of hydrogen or a mixture ofhydrogen with other gas(es) through the interior of the component, itbeing the permeation of the hydrogen via the wall of the component thatcauses the hydridation of the material, iii) heating of the component bythe Joule effect, iv) determination of the power dissipated by thehydridation reaction as a function of time, of the dissipatedhydridation energy measured during the process, and of the electricresistance in the component by means of: iv.1) the voltage drop alongthe component, and iv.2) the variation in electric current applied formaintaining its temperature at the predetermined value for thehydridation reaction.
 2. Device for carrying out the measurement methodof hydridation kinetics at different temperatures, in industrialcomponents such as tubes and tubular claddings of metallic elements,metal alloys and any other material with and without protectivecoverings, wherein it comprises the following elements: a) a high orultra-high vacuum chamber in which the component to be analysed isinserted, b) a gas line for causing hydrogen or a mixture of hydrogenwith other gas(es) to pass through the interior of the component, c)heating systems by the Joule effect, thermocouples and systems fortemperature control in the component, and d) two electrodes in the formof a ring or other well-defined geometry, arranged symmetrically andequidistant from the central thermocouple.
 3. The method according toclaim 1, wherein the measurements of hydridation kinetics are made inindustrial components of metallic elements, metal alloys and any othermaterial with and without protective coverings.
 4. The method accordingto claim 3, wherein the industrial components are tubular, among others,the tubes and tubular claddings for fuel in the cores of nuclearreactors.
 5. The device according to claim 2, wherein the measurementsof hydridation kinetics are made in industrial components of metallicelements, metal alloys and any other material with and withoutprotective coverings.
 6. The device according to claim 5, wherein theindustrial components are tubular, among others, the tubes and tubularcladdings for fuel in the cores of nuclear reactors